Entrelac in the round

I am planning on making a twin size afghan using entralac in the round. I know
that 7 squares will make that size. What I am trying to determine is how many
squares total will there be (width and height). I want to use 4 colors-off white
and 3 shades of blue. Starting with the off-white, then do rounds in each of the
shades of blue. However, I am not sure how many rounds to do of each color so
that it will come out symmetrical. Can anyone help me?

I'm not sure what you mean by '7 squares will make that size'. A twin mattress is 39" x 75". You will need some some overhang for a useful blanket, let's say 1 foot all around, so 61" x 87". This blanket is 26 inches longer than it is wide. You will need a starting row of squares 26 inches wide (however many squares that comes to with your yarn hook and tension). Since you will be adding rounds of equal size on each of the 4 sides, the blanket will always be 26" longer than it is wide, not counting that first row.

If your squares were 1", you'd have to add 30 rounds to the center row (30 rows x 1" on either side of the center, width wise, plus the center row, gives you the width of 61"). Therefore, you'll need to swatch to answer your question.

That's what I use when making entrelac blankets in the round as opposed to working corner to corner or edge to edge. My favorite combination was white, grey and black. It turned out beautifully!

>>>Why are you working a "flat" piece/afghan "in the round"

It's the same concept as working anything else that's flat. With this, you aren't going in a circle, you're starting at one point and working your way around back to that point and then changing colors, kind of like working a granny square in the round. I hope that makes sense.